1. Field of the Invention
This invention relates to devices incorporating ultrasound transducers, and more particularly to an ultrasound transducer device for the continuous imaging of body organs.
2. Background
Ultrasound technology is widely used for imaging various organs in the body and for diagnosis of tissue pathology. A variety of ultrasound transducer devices is currently available for imaging specific areas of the body. These transducer devices vary in size, shape and operating frequency depending on the age, body size of the patient and the organ that has to be imaged.
Most ultrasound examinations are performed by placing a transducer on the body surface of the patient. However, transducers may also be placed in body cavities such as the rectum and the vagina to image various abnormalities in these structures. More recently, transesophageal echocardiography has been performed by mounting a transducer at the tip of a gastroscope and introducing it into the esophagus. Transesophageal echocardiography can be used for prolonged monitoring of heart function, e.g. during open heart surgery. However, the inconvenience of swallowing the probe, the potential for complications as well as the expense, limit its use.
Commonly, in the experience of the inventors, ultrasound examinations are performed mostly by placing a probe containing an ultrasound transducer on the surface of the patient's body. This is done to make a specific diagnosis and not for prolonged monitoring of patients. An explanation for this is that the probes usually must be held by someone against the patient's body. Also, the narrow and long shape of the transducer probe precludes proper motion-free positioning for long term use. Furthermore, patient motion is restricted by the transducer probe, i.e., the patient will not be able to turn to his left when a long transducer probe is placed below the left nipple. Clancy et al in U.S. Pat. No. 5,022,410, describe an ultrasound transducer device which holds the transducer in a fixed position relative to the patient's body. They describe a device with a flexible and elongate arm which has a mount for a transducer and a means for locking the arm in a fixed position. This device however is not ideally suited for cardiac imaging, because the transducer end of the device is not designed to fit snugly into an intercostal (between ribs) space, and because even slight movements of the transducer will result in loss of or inadequate imaging for diagnostic use. Further, there is no apparent means of correcting the position of the transducer once the arm is locked in position.
A review of currently available transducer probes and the pertinent patent literature shows that none of the devices are conducive to fixation of the probe on the chest wall, and for patient comfort, for monitoring over prolonged periods of time.
In the experience of the applicants in the field of cardiology, there are several desirable potential applications for continuous imaging of the heart chambers and left ventricular function in a manner beneficial to the patients. These include:
a) Intraoperative Monitoring: Monitoring of left ventricular function during non-cardiac surgery in patients with known coronary artery disease, has long been advocated to detect and treat early myocardial ischemia. This treatment could prevent the development of serious complications such as myocardial infarction and possible death. The current method of monitoring such patients is by transesophageal echocardiography. Monitoring of left ventricular function with a transducer attached to the surface of the chest would be much more convenient, less expensive and would be routinely used. PA1 b) Stress Echocardiography: Stress eehocardiography practice involves ultrasonic monitoring of left ventricular wall motion during exercise, using a hand held transducer probe. The appearance of a wall motion abnormality indicates the presence of myocardial ischemia. Ultrasonic images obtained during exercise are often suboptimal because of excessive motion of the transducer. A transducer attached to the chest wall would greatly improve the quality of the images obtained and improve the sensitivity of this technique for detection of myocardial ischemia. PA1 c) In the Coronary Care Unit: Left ventricular function is a major determinant of morbidity and mortality in patients susceptible to heart attack. Continuous monitoring of left ventricular function in a coronary care unit is greatly desirable for timely preventive action, but is not currently available. An ultrasound device attached to the chest wall of the patient would facilitate continuous monitoring of left ventricular function and improve therapeutic decisions. For instance, if a large area of the patient's left ventricle stops moving during an episode of chest pain, this implies a severe proximal stenosis of a major coronary artery. Urgent cardiac catheterization and angioplasty or bypass surgery is indicated to prevent permanent damage to the heart leading to heart failure and death. PA1 d) Cardiac Catheterization: Continuous monitoring of the heart walls and heart valves with an ultrasound transducer probe attached to a patient's chest wall may facilitate the conduct and monitoring of invasive procedures. For example, during catheter balloon commissurotomy for mitral stenosis, proper positioning of the balloon across the mitral valve may be achieved by ultrasonic imaging. PA1 e) Imaging the Inferior Vena Cava: Continuously imaging the inferior vena cava from a subcostal position may help to assess hypovolemia resulting from hemorrhage. Collapse of the inferior yens cava indicates a severe hemorrhage. Return of the inferior vena cava to normal dimensions would indicate adequate volume replacement.
Continuous recording of left ventricular ejection fraction is also feasible using an ultrasound transducer.
Besides cardiac imaging, there are other areas of body diagnosis which would benefit from the use of an ultrasound transducer being attached to the body surface. For example, a transducer device could be placed on the abdomen to monitor laparoscopy.
In view of the foregoing potential applications, it would be a significant medical diagnosis and monitoring advance over presently available techniques, to provide an ultrasound transducer device for continuous imaging of the heart and other body organs.